Method of producing oscillations from piezo electric plates



NOV. 3, 1931. AHUND 1,830,322

METHOD OF PRODUCING OSCILLATIONS FROM PIEZO ELECTRIC PLATES Filed Sept. 30, 1925 Patented Nov. 3, 1931 UNITED STATES PATENT OFFICE AUGUST HUND, OF BETHESDA, MARYLAND, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

I FEDERAL TELEGRAPH COMPANY, .11. CORPORATION OF CALIFORNIA METHOD OF PRODUCING OSCILLATIONS FROM PIEZO ELECTRIC PLATES Application filed September 30, 1925. Serial No. 59,675.

My invention relates broadly to electrical systems and more particularly to the production of constant frequency electrical oscillations from piezo electric bodies.

One of the objects of my invention is to provide a constant frequency generator for electrical oscillations where piezo electric plates are employed for maintaining the frequency of the generator constant at all times.

Another object of my invention is to provide a piezo electric crystal system which may be conveniently employed for the production of low frequency oscillations without the necessity of providing piezo electric plates 5 of inconvenient size and weight and of unreasonable cost.

Still another object of my invention is to provide a circuit arrangement in which a pair of high frequency piezo electric crystals are employed and the oscillations thereof reduced in frequency for the production of low frequency oscillations under control of piezo electric crystals and conveniently employed for various purposes.

A still further object of my invention is to provide a system for producing oscillations from a pair of piezo electric crystals of a frequency lower in order than the two original frequencies in such manner that relatively small crystals may be employed for the production of constant low frequency oscillations.

Still another object of my invention is to provide a method of producing low frequency oscillations from a single piezo electric plate of relatively small size.

A further object of my invention resides in the employment of piezo electric plates for reducing the frequency of electrical oscillations under control of piezo electric plates.

My invention will be more clearly under stood from the following specification by reference to the accompanying drawings, in which:

Figure 1 illustrates one method which I employ for reducing the frequency of electrical oscillations under control of a plurality of piezoelectric plates; Fig. 2 shows a modified circuit arrangement which I may employ for securing low frequency oscillations from piezo electric plates; Fig. 3 shows another circuit arrangement I may employ in producing low frequency oscillations from relatively small piezo electric plates; Fig. 4 illustrates a piezo electric plate of small size ground in accordance with the principles of my invention for the production of low frequency oscillations; and Fig. 5 is a drawing similar to t but illustrating the electrical connections thereto.

In my copending application Serial No. 59,677 filed September 30, 1925, I have described a method of cutting piezo electric plates which will have predetermined and uniform frequency characteristics. The fundamental frequency obtainable from a piezo electric plate of rectangular or circular form follows an. empirical law which may be expressed by the following formula:

where t represents the thickness of the piezo electric plate in millimeters (mm) and 7 represents the frequency expressed in kilocycles (kc.) per second. From observation of this formula it is apparent that a very thick plate would be required to produce audio frequency oscillations. This plate would normally have such a thickness that it would be impracticable to employ a piezo electric plate as a constant frequency generator of low frequency currents for precision work. By my invention I render practical the use of piezo electric plates as audio frequency generators and am enabled to secure the benefits of the constant frequency characteristics of such plates by circuit arrangements and a novel method of grinding the crystals.

I may secure the production of low frequency currents by providing two high frequency piezo electro plates where the desired frequency is the difference between the frequencies of the two piezo electric plates. These plates may be connected to control independent oscillatory circuits, the effects of which are impressed upon a common or a third circuit. The plates may be parallel connected to control the same electron tube system by the resultant low frequency beat note between the high frequency oscillations or a relatively thin piezo electric plate may be ground in stepped formation in such manner that one portion of the plate tends to oscillate independently of another portion of the plate at separated high frequencies which beat with each other to produce a frequency of an order lower than the two original frequencies which is the difference in the frequencies produced by the separate portions of the plates.

Referring to the drawings in more detail, reference characters 1 and 2 designate two separate piezo electric plates each having high frequency oscillatory characteristics. The-piezo electric plates are chosen such that the respective high frequency currents thereof are separated by a difference in frequency which is equal to the frequency of the oscillations which it is desired .0 produce. The piezo electric plate 1 is arranged to control an electron tube 3 having grid electrode 3a, plate electrode 3?) and filament electrode 30. The cathode 30 is heated from battery A under control of rheostat 4. The output circuit of the tube 3 includes the plate electrode 3?), inductance 5, shunted by tuning capacity 6, high potential battery B, ammet-er 7 and test telephones 8. A by-pass condenser 13 is shunted around battery B, ammeter 7 and test telephones 8 for by-passing high fre quency oscillations. The grid circuit of the tube 3 from grid electrode 34: connects through the piezo electric plate 1 secured between plates 9 and 10 with the switching device 11. The switch arm 12 may be connected with either contact 14 or 15 to connect the quartz plate 1 between the grid electrode 3a and the filament electrode 30 or the grid electrode 360 and the plate electrode 3?). The slab of quartz 1 is used for converting mechanical vibrations in o oscillations and the oscillator circuit is adjusted to resonance by the tuned system 5-6. A feed back arrangement is provided by which sustained oscillations are possible. The quartz plate can either be inserted between the grid and filament electrodes or between the grid and plate electrodes Where the circuit is used for the generation of oscillations of different frequencies. For example, the'insertion of the piezo electric plate between the grid and plate electrodes gives usually better resul s for currents over 300 kilocycles, while for frequencies below this the insertion of the piezo electric plate between the grid and filament electrode seems to give bet er results.

Upon completion of the electron tube circuit as described the value of the capacity 6 and inductance 5 maybe varied, resulting in the settin up of a transient current whose decay assumes a frequency which is governed by the period of a possible mechanical vibration of the quartz plate. Normally the oscillation will turn into a damped wave train and die out before being observed. If, however, the self-induction of coil 5 of proper magnitude is inserted in the plate circuit, it will, on account of its inertia, effect and feed back through the tube and itself render the circuit regenerative. That is to say, a negative resistance action is produced between the grid and filament electrodes and as such sustains the vibrations due to the quartz. Vvhenever this happens the plate current indicated by the direct current meter 7 drops to a certain minimum value. The output is considerably increased by use of variable condenser 6 in parallel wi h the inductance 5 of the plate branch. Where the quartz plate is connected between the filament and the grid, the condenser 6 is set in its minimum capacity position and its capacity is gradually increased. For a certain setting, the oscillations begin to build up and while increasing the capacity 6, the plate current will keep on decreasinguntil close to the resonance setting of the 5-6 circuit the oscillations stop altogether.

For thequartz plate connected to the plate and the grid electrodes, the capacity 6 has to be gradually decreased from the maximum setting in order to start the oscillations. The building up of the oscillations takes place normally in a fraction of a second but in some cases it may require several seconds and it is then'necessary to slowly change the capacity 6. The slow action may be due to either a poor piece of quartz, an unfavor: able magnitude of the inductance 5 or the lack of necessary freedom of the quartz plate for oscillator actions, while for the use as a resonator the conductive layers can even be part-ed on the quartz or clamped against it without disturbing the operation.

The piezo electric plate 2 is connected in an electron tube circuit similar to the arrangement of the electron tube circuit of tube 3. I have illustrated corresponding parts by means of prime characters.

In Fig. 1 of the drawings, I have shown the inductances 5 and 5 magnetically coupled by which the oscillations developed by piezo electric plates 1 and 2 act upon each other to develop a beat frequency equal to the difference of the frequencies of piezo electric plates 1 and 2. In this manner piezo electric'plates of relatively small thickness each having a high natural frequency characteristic are so arranged as to secure a re duction in frequency for producing the frequency of an order lower than the two original frequencies. The low frequency oscillations may be taken off from, either one of the two frequency circuits.

.Tn Fig. 2 I have illustrated another circuit arrangement for the separate piezo electric plates where an intermediate circuit 16 is provided having windings 17 and 18 coupled withinductances 5 and 5 andconnected in an oscillatory circuit tuned by means of condenser 19 to the two low frequencies of piezo electric plates 1 and 2. The charact ristics of the third circuit 16 are such that a current of the beat frequency of the piezo electric plates 1 and 2 may be emphasized. That is to say, the oscillation constant CL of the ciruit 16 satisfies the resonance condition in the formula:

\Vhere f=f 72, where f represents the he quency of piezo electric plate 1 and f represents the frequency of piezo electric plate 2. When the piezo electric plate is connected between the filament and the grid the tuning should be such that the combined iinpedauc acts like an inductance while for the connecion of the piezo electric plate between the g id and the plate electrodes the branch circuit should have an oscillation constant somewhat lower than required by the resonance a/L0 and such that the combined effect of capacity and inductance is somewhat capacitive.

In Fig. 3 I have shown another method for producing low frequency oscillations under control of high frequency piezso electric plates. An electron tube 20 is provided having grid electrode 20a, plate electrode 20?), and lila- Inent electrode 200. The filament electrode 200 is heated from battery 21. The output circuit of the tube 20 contains units as heretofore described in connection wi h Figs. 1 and 2, that is, high potential battery B, indieating meter 7, and test telephones 8 shunt ed by condenser 13. Inductance 5 shui ed by tuning condenser 6 comprises the tuning ele ment for the oscillatory system. Piezo electric plates 1 and 2 are connected in parallel and in one and the same circuit 2; which generates directly the current of the desired low frequency by interaction of the frequencies developed by each of the plates.

In a divisional application Serial I? 1%,- 383, filed February 15, 1927, issued as Patent No. 1,717,451, on June 18, 1929, clain h ve been drawn covering these and other feat of the disclosures shown and described i1- this parent application.

In Figs. 4- and 5 I have illustrated a method by which I am able to obtain a relat' low frequency from a piezo electric of relatively small size. The piece plate 23 comprises portions ant. of different frequencies formed tep 25. The size of the plate has been exaggerate, for the purpose of illustrating the princi ile of the invention and it will be understood that the step 26 is extremely small. The plate 23 is interposed between metallic conductive plates 27 and 28 which are connected to any desired oscillator or control circuit, for example, to the oscillator circuit of Fig. 3. It is not necessary that the conductive plates 27 and 28 actually contact with all of the surfaces of the piezo elect ic plate 23 but that the plates merely be in capacitive relation with respect to the piezo electric plate. The high frequency oscillations of the independent portions 24 and 25 of the piezo electric plate :23 react with each other for developing oscillations of a frequency lower in order than the two original frequencies. By the methods described herein it is practical to produce audio frequency oscillations from piezo electric plates of small size. These oscillations are constant in character and may be employed for various purposes. It will be understood that piezo electric plates may he cut with several steps or two steps as above and such that the difference in frequency between the respective portions produces a high frequency. In this way one quartz plate could be used for producing many fundamental standard frequencies The steps may be cut in other faces of the plate than as indicated in Fig. lVhile I have described the principles of my invention in certain particular embodithat it be unc stood that s may be made and .i It I in end upon the invention other than by the scope of the appended l hat I claim and desire to secure by Let- Patent of the United es is as follows:

1. In a system for producing constant frequency oscillations, the combination of a pair of independent electron tube circuits, piezo electric plates connected with each of said electron tube circuits and arranged to develop high frequ cy oscillations in said electron tube circuits differing from each other, a circuit coupled to each of said electron tube circuits and arranged to receive the oscillations developed by each of said piezo electric plates whereby said oscillations react to produce a beat frequency of constant char-- acteristics.

2. In a system for the production of constant frequency oscillations, the combination of a pair of electron tube circuits each including input and output circuits, piezo electric plates having different frequency characteristics connected in the input circuits of saic. tube circuits and arranges to control the frequency of the oscillations developed by said elr .on tube cir nits, and means whereby the di .rent frequencies thus produced act upon each other for deriving); a beat freelectric crystals connected to the control electrodes of said electron discharge devices. tuned circuits connected to the anode electrodes of each of said electron discharge devices, and a tuned circuit coupled to each of said tuned circuits for developing electric oscillations through the interaction of the oscillations generated by said electron discharge devices.

4. In an electron discharge device system of the class described the combination of a plurality of electron discharge devices, piezo electric crystals connected to the control electrodes of said electron discharge devices, circuits connected with said electron discharge devices for developing piezo electric crystal frequency controlled oscillations therein and for developing oscillations of a lower frequency through the interaction of said piezo electric crystal frequency controlled oscillations.

5. In an electron discharge device system of the class described the combination of a plurality of electron discharge devices having grid, cathode and anode electrodes, a plurality of piezo electric crystals, connections between said piezo electric crystals and the grid electrodes of said electron discharge devices, a ne work including the anode electrodes of said electron discharge devices for developing oscillations of a lower frequency than the frequency of the oscillations developed in said circuits through the interaction of said last mentioned oscillations.

6. An oscillation circuit including an electron tube and a piezo-electric device vibrating at one frequency, and another oscillation circuit including another electron tube and another p ezo-electric device vibrating at a different frequency, said circuits including means for deriving therefrom a frequency equal to the difference between the two firstinentioned frequencies.

7. A system for the production of oscillations of low frequency comprising means for generating oscillations of two different frequencies, said means including one circuit having a piezo-electric device and a space discharge tube associated therewith and another circuit having another piezo-electric device and a space discharge tube, and means for combining said oscillations for producing oscillations at their frequency difference.

8. A piezo-electric audio-frequency resoua' or including a plurality of high-frequency piez0-electric devices having frequency characteristics, the difierence of which is equal to said audio frequency. independent oscillatory circuits associated with said piezo devices, and a common audio-frequency oscillatory circuit controlled by said independent circuits and said piezo devices 9. A generator of low frequency oscillations comprising two high frequency oscillator networks of each including a space discharge tube and a piezo electric frequency controlling device, and a circuit co-operative- 1y controlled-by the two said networks for deriving their difl'erence fr uency.

In testimony whereof I a x my signature.

AUGUST HUN D. 

